The present invention relates to new thiophosphoretted compounds soluble in the mineral oils obtained by reacting at least one phosphorus sulfide with at least one detergent sulfonate known as "surbasic".
In a general way, a surbasic detergent sulfonate can be defined as composed of a surface-active agent essentially consisting of an alkaline or alkaline-earth salt of a sulfonic acid comprising oleophilic groups and keeping in colloidal dispersion salts of mineral weak acids such as CO.sub.2, H.sub.2 S and alkaline or alkaline-earth bases.
According to the invention, the product of the reaction between the phosphorus sulfide and the surbasic detergent sulfonate can be optionally treated by at least one active hydrogen compound which may be water, an alcohol, a phenol, a carboxylic acid, an ester-acid, a mineral acid, a mineral base, an amine, an amide or a mercaptan.
The present invention also relates to the preparation of these new thiophosphoretted compounds and to their use as additives in mineral and synthetic lubricants. In particular, it has been discovered that these new additives show antiwear and extreme-pressure properties which are very interesting for use with motor oils, gear oils, hydraulic fluids, lubricating greases or metal-working oils.
Antiwear and extreme-pressure additives are added to lubricants when intended for lubricating parts subjected to heavy mechanical stresses, such as the distribution in thermal engines, gears, bearings or thrusts. Heavy mechanical stresses also appear during the machining of metals, be it cutting or forming.
The antiwear additives which are most widely used in engines are the zinc dialkyldithiophosphates, but the efficiency of these additives is reduced by the presence of nitrogenated dispersers, probably because of the forming of coordination complexes between these two types of additives. Modern motor oils require large amounts of dispersers to be in accordance with the VE test of the SG specification of the American Petroleum Institute. The higher additive content which is necessary to keep the antiwear qualities constant leads to an increase in the phosphorus content in the motor oils, whereas it is precisely the contrary which is sought after for maximum efficiency of the catalytic mufflers intended for reducing the pollution caused by the exhaust gases.
As for transmission oils, two types of additives are widely used: the phosphosulfurized additives and the additives based on potassium borate dispersion. The main drawback of mineral oils containing phosphosulfurized additives is their thermal instability, which begins to show as low as 120.degree.-130.degree. C. As a matter of fact, it is not unusual to reach temperatures of 150.degree. C. in the transmissions of heavy-duty vehicles or of private cars used in severe conditions. Transmission oils based on potassium borate clearly show a greater thermal stability, but they are water-susceptible, which may represent an obstacle for certain uses. More efficient antiwear and extreme-pressure additives with a higher thermal stability and showing less interactions with the other additives in the formulations are actively searched for.